Atomistic origin of nonlinear bistable domain wall dynamics in double-notched Ni nanowires

The dynamics of magnetic domain walls (DWs) in nanowires are strongly influenced by geometrical pinning, which defines the effective energy landscape governing their motion. In this work, we investigate the role of atomic-scale effects on the pinning behavior of DWs in double-notched nickel nanowires using large-scale atomistic spin dynamics (ASD) simulations and compare the results with micromagnetic modeling. While micromagnetic calculations predict a predominantly single-well pinning potential for small notch separations, ASD reveals the emergence of a double-well energy landscape originating from localized atomic-scale interactions at the constrictions. The atomistically obtained pinning profiles are subsequently incorporated into a collective-coordinate model to investigate their dynamical consequences. We find that the atomistic double-well potential induces chaotic domain-wall motion and strongly nonlinear responses under oscillatory magnetic fields. This demonstrates that atomic-scale features can qualitatively modify the effective energy landscape governing domain-wall motion, with important implications for the design of nanoscale spintronic devices based on controlled pinning and switching.